Vehicular Networks facilitate communication among vehicles to notify and exchange road-related information and thereby, ensure road safety. In VANETs', the network infrastructure provides a facility to generate the messages. But all such messages need not be reliable. Therefore, in order to build reliability on the message, the vehicle in which the message was generated can be evaluated based on a reputation score that it has earned during its prior transmissions. This paper aims to design and analyse a reputation system for VANET's which aids the receiving vehicle to decide the reliability on the message based on the score that has been earned by the transmitting vehicle.